Wireline, electric line and slickline are commonly used in oil and gas wells to deliver strings of tools to a desired location in a wellbore. The wireline string is suspended from a wire or an electrical cable or the like, and is lowered into the well from a winch located at the surface. The wire is spooled out until the tool string is at the desired depth in the wellbore, and the tools are then deployed. Wireline tool strings have many purposes, and in the context of the present invention, many different wireline tools can be used without departing from the scope of the invention. Likewise the nature of the cable (plain wire or electrical cable or some other conduit) can be varied in the context of the present invention without departing from its scope.
Wireline tool strings commonly include a roller device, typically having rollers such as wheels protruding from a body, so as to engage the inner surface of the casing of the wellbore in which the tool string is deployed, and reduce the friction between the casing and the tool string as the tool string moves into and out of the well. This increases the reach of the tool string, particularly in deviated wellbores. Existing designs of wireline roller tool typically favour large diameter wheels, for stability and so that the roller device rides easily over lips at the junctions between adjacent stands of pipe.
US2008/0264639, US2008/0164018, US2006/0070733 and U.S. Pat. No. 7,434,627 are useful for understanding the invention.